The present invention relates generally to automatic transmissions, and more particularly, to an accumulator piston used therein. Specifically, the invention relates to an improved so-called 1-2 accumulator piston, which is made and assembled into one piece from two pieces, and which includes two seals bonded to the piston. This arrangement is advantageous from the standpoints of simplicity, reliability, and installation in the intended application.
As currently manufactured, one form of the 1-2 accumulator piston includes two O-rings as the seal. By switching to a welded component having two deep-drawn cups separately formed and then butt-welded together, with the seals being bonded on to the stampings or casings, an improved product is made.
Basically, the 1-2 accumulator piston in prior art transmissions has either been an aluminum casting or forging or a plastic piston. In the case of the aluminum casting or forging, two loose lip seals or O-rings were used. In the case of the plastic piston, two loose lip seals or O-rings were also provided. The aluminum casting approach had the disadvantage of being more expensive, because of the machining required on several surfaces. The aluminum casting, in addition, was heavier and in some cases less accurately machined. The loose lip seals were not as durable as bonded seals. In addition, the problem of a fit in the bore was presented. A machined aluminum casting or forging with loose O-ring seals had the further disadvantage of galling in the steel or aluminum bore formed in the housing.
In the case of plastic, the strength was questionable as regards the piston. This shortcoming was particularly apparent over the life of the product, which could easily exceed 100,000 miles or perhaps, even two or three times that amount. Prior art plastic cups simply did not have the potential life expectancy of a more substantial piston. The invention does away with the need of O-ring or other loose lip seals, replacing them with bonded seals having several advantages.
A one-step assembly process is possible with the design, which includes a major diameter flange on one cup and a smaller diameter flange on the other cup, with the two cups being deep drawn and welded together at the interface. The resulting metal piston is much stronger than prior art designs, it is lighter, more durable, and less expensive.
In view of the failure of the prior art to develop an accumulator piston of an advantageous type, it is an object of the present invention to provide an improved accumulator piston.
Another object of the present invention is to provide a one-piece component in place of components having O-rings or other loose-fitting seals.
Yet another object of the present invention is to provide a bonded accumulator piston and seal unit requiring no additional assembly operations by the end user, that is, the labor force at the automatic transmission assembly point.
Still another object of the invention is to make housekeeping easier for the user, in the sense of taking up less warehouse space with separate components requiring assembly and subsequent fitting.
It is a further object of the invention to provide an element which, in use, will avoid undue pinching of rubber elements. In this connection, a dual molded lip is more durable and less likely to be torn or otherwise damaged in use than are O-rings.
In particular, it is an object of the invention to locate the seals on the part where they will not engage the ports or openings in the bores during the assembly process.
A still further object of the invention is to provide a piston wherein scoring or galling of the running surfaces can be avoided, particularly those where there would be metal-to-metal contact in the event of misalignment in either aluminum or steel housings. By way of explanation, when a non-bonded O-ring moves in the groove in which it is located, it eventually becomes torn or breaks down. Metal-to-metal contact then occurs. This occurs with every non-bonded O-ring. When there is misalignment, wear is accelerated.
An additional object of the invention is to provide reduced stresses and strains and increased fatigue life over the expected life of the unit.
Yet another object of the invention is to provide a lower cost assembly compared with an aluminum forging or casting.
Still another object of the invention is to provide easier installation than is attainable with constructions containing O-rings.
More specifically, another object is to avoid the presence of O-rings, which, during installation, and thereafter, are more easily cut by the passages in the bores, creating questionable installation reliability.
A further object of the invention is to avoid scuffing and galling of the parts relative to each other.
A still further object of the invention is to do away with scuffing of the bore surface by reason of having rubber-to-metal contact rather than aluminum-to-steel contact in the area of the bores or, in the alternative, with aluminum-to-aluminum to contact in the bore.
The above advantages of the invention are achieved in practice by providing a bonded piston, preferably laser welded and made from two deep draws, with the open sides of the draws being directed oppositely and with each end portion of the piston having its own associated seal bonded thereto.
The exact manner in which the foregoing invention is achieved in practice will become more clearly apparent when reference is made to the following detailed description of the invention set forth by way of example and shown in the accompanying drawings, in which like reference numbers indicate corresponding parts throughout.